The present invention relates to a photothermographic material, a preparation method thereof and a coating apparatus for use in the preparation thereof, whereby photothermographic material exhibiting superior photographic performance and storage stability, also having a layer strength sufficient to cause no abrasion mark, without causing uneven or non-uniform coating or coating coagulation.
In the field of medical treatment and graphic arts, there have been problems in working property with respect to effluents produced from wet-processing of image forming materials, and recently, reduction of the processing effluent is strongly demanded in terms of environmental protection and space saving. Techniques meeting such demands are known, for example, as a method described in U.S. Pat. Nos. 3,152,904 and 3,487,075; and D. Morgan xe2x80x9cDry Silver Photographic Materialxe2x80x9d (Handbook of Imaging Materials, Marcel Dekker, Inc., page 48, 1991). Such photosensitive materials are usually thermally developed at a temperature of not less than 80xc2x0 C., which are also called thermally developable photothermographic materials.
Most of such types of photothermographic materials have been manufactured through solvent-based coating, because in a light sensitive layer formed by coating an aqueous mixture of a developing agent and an organic silver salt, a water-mediated oxidation-reduction reaction gradually results, leading to an increase in fogging. Accordingly, there have been sought antifoggants but a useful one has not been yet obtained.
In water-based coating, an improvement or modification of binders has been attempted to reduce the moisture content in the dried layer. One technique thereof is the use of a hydrophobic latex capable of forming a coating layer exhibiting a reduced moisture content, as described in JP-A No. 10-207001, 10-221807, 10-221806, 11-119375 and 11-288068 (hereinafter, the term, JP-A means an unexamined, published Japanese Patent Application). However, to form a coating layer having a relatively low moisture content, sufficient drying is needed, disadvantageously retarding drying time.
Even in solvent-based coating, polar solvents are generally employed to enhance solubility of photographic additives and not a little water is carried therein, having an undesirable effect. Further, a silver halide used in the photothermographic material is formed in a water-based medium so that the photographic material necessarily contains a small amount of moisture, resulting in the undesirable influence of moisture.
Binder resistant to the influence of moisture contain no group capable of cross-linking, such as an amino or carboxy group, so that hardening agents capable of forming cross-linkage with the amino or carboxy group cannot be employed therein, leading to relatively low layer strength and leading to the disadvantage of being easily abraded. A technique for forming a coating layer exhibiting sufficient layer strength minimally affected by moisture is therefore desired.
In view of the foregoing, the present invention has been made and it is an object of the present invention to provide a photothermographic material exhibiting superior photographic performance, storage stability and moisture resistance, and not easy to be abraded, which is capable of compensating deteriorations in various performance, caused by limitations in the manufacturing process; and a manufacturing method and an apparatus for obtaining it.
The object of the invention can be accomplished by the following constitution:
A photothermographic material comprising on a support light sensitive silver halide grains, an organic silver salt, a reducing agent and a binder, wherein the photothermographic material further comprises a silane compound represented by formula (1) or (2):
formula (1):
(R1O)mxe2x80x94Sixe2x80x94[(L1)x
R2]nxe2x80x83xe2x80x83formula (1):
formula (2) 
wherein R1, R2, R3, R4, R5, R6, R7 and R8 represent each an alkyl group, an alkenyl group, an alkynyl group, an aryl group or a heterocyclic group, which may be substituted; L1, L2, L3 and L4 represent each a bivalent linkage group; m and n each are an integer of 1 to 3, provided that m+n is 4; p1 and p2 are each an integer of 1 to 3 and q1 and q2 are each 0, 1 or 2, provided that p1+q1 and p2+q2 are each 3; r1 and t are each 0 or an integer of 1 to 1000; and x is 0 or 1.
U.S. Pat. Nos. 4,828,971 and 5,891,610 describe the use of a polysilicate compound. However, such a compound exhibits hydrolysis resistance higher than a polyalkoxysilane but has a disadvantage that the resulting dry layer easily causes cracking. With regard to modification of the layer surface of photothermographic materials, U.S. Pat. Nos. 3,489,567 and 3,885,965 disclose incorporation of a polysiloxane compound as a lubricant. However, such a compound enhances lubrication but does not enhance the surface layer strength of the photothermographic material, enough to improve abrasion resistance. Further, U.S. Patent discloses a silane compound to improve adhesion between a protective layer and a light sensitive layer. However, any of of the foregoing is distinct from the object, effects or the compound of the invention.
According to this invention, it was found that the use of a silane compound having a specific structure led to enhancements in photographic performance and layer strength. It was further found that the use of the compound relating to this invention enables uniform coating at a high speed by modification of a coating system.